Pulsars could help unravel space-time

A pulsar and a neutron star whirl around each other in this illustration. Click on the image to download a 4-MB animation of their cosmic dance.

CSIRO / John Rowe Animation

The discovery of a pulsar in a faint double-star system is giving scientists new hope of glimpsing one of nature's most elusive phenomena: gravity waves. While their existence has been inferred indirectly, scientists have yet to come face-to-face with these warpings and billowings of space-time that Einstein predicted in 1918 as a fundamental consequence of his theory of general relativity. Massive objects moving at extreme speeds, the theory explains, create ripples in the very fabric of the universe — ripples that, if detected, will help confirm Einstein's elegant vision of the workings of the cosmos.

Compact objects like neutron-star binaries are just the kind of cosmic dancers capable of shaking up space-time. As they tauntingly spiral toward one another, neutron stars give off energy in the form of gravitational radiation. Recently discovered pulsar J0737-3039 and its neutron-star companion now are engaged in the closest, fastest tango of any neutron-star system ever observed, orbiting one another once every 2.4 hours. The pair was discovered by a team of scientists from Italy, Australia, the United Kingdom, and the United States using the 64-meter CSIRO Parkes radio telescope in eastern Australia.

The 64-meter Parkes Radio Telescope has been hard at work since 1961. A movable 18-meter radio dish seen here in the background assists with interferometry studies.

John Sarkissian / CSIRO

The team found that this system is moving much faster than, for example, the Hulse-Taylor pulsar — the first neutron-star binary ever detected, which has an orbital rate of 7.75 hours. It was discovered in 1974, winning Russell Hulse and Joseph Taylor of Princeton University a Nobel Prize. Since this discovery, only one other system capable of producing significant gravitational radiation has been found. That made the outlook for catching gravity waves rather bleak. So when LIGO (the Laser Interferometer Gravitational Wave Observatory) set out to do just that, many were skeptical of its chances.

Now, the prospect of detecting gravitational waves appears much more favorable. Because the newly discovered neutron stars are orbiting one another so quickly, the system's life span will be significantly shorter than those of its two predecessors. These stars are expected to complete their dance eighty-five million years from now, when they will collide. Of course, that in itself is not entirely helpful, given that it is only in the last two or three minutes before they merge that they will produce gravity waves strong enough for LIGO to register. But the finding suggests that this type of tight, fast, and relatively short-lived system actually is common in our Milky Way — and much more common than binaries like the Hulse-Taylor.

Two neutron stars merge in this illustration.

CSIRO / John Rowe Animation

"This is a very faint system and the pulsar's spin period is very short, only 22 milliseconds, which makes it very hard for observers to find compared to the Hulse-Taylor," says Northwestern University's Vicky Kalogera, a member of the team who made the discovery. "So if we have something that is easy to discover and we find only one and we have something that is difficult to discover and we also find one, then in the second case, there are probably many more of these in the galaxy."

In fact, the new data boosts the neutron-star merger rate by a factor of six or seven, which means LIGO should be able to detect such an event once every year and a half, a vast leap from previous estimates of only one every ten or twenty years. And if that's the case, we won't have long to wait to witness firsthand the extraordinary rolling landscape of Einstein's universe.